Pressure switch



July 30, 1946. M. w. HUBER 2,404,843

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Patented July 30, 1946 PRESSURE SWITCH Matthew W. Huber, Watertown, N.Y., assignor to The New York Air Brake Company, a corporation of NewJersey Appiication July 27, 1944, SerialNo. 546,797

(Cl. 20G-83) 3 Claims.

This invention relates to pressure switches, and particularly to apressure actuated switch of the micro-motion type.

There are available several commercial switch mechanisms of the snapaction type, which are characterized by the ability to handle ratherlarge currents and which shift reversely in response to motion of theactuating member (usually a plunger) through a very small range.

Fluid pressures up to four or five thousand pounds per square inch arein commercial use today and the trend is upward. A spring loadedabutment subject to such pressures may have a rather small range ofmotion, say 3/54 and still afford several times the motion required toactuate such a switch. The invention takes advantage of this fact byinterposing between the abutment and the switch a variable ratio levermechanism which changes the distance the abutment must move to trip theswitch. If the required motion is small, the sensitivity is said to behigh. The ability to adjust sensitivity facilities precise setting ofthe device for particular conditions.

For large adjustments of sensitivity the switch is shifted relatively tothe lever fulcrum. This can be done in various ways but in the exampleillustrated the switch is simply reversed on its mount changing thepoint cf engagement of the switch plunger with the lever. For smallerchanges of sensitivity the fulcrum is shifted. The fulcrum adjustment isso contrived that the trip point of the switch, relatively to the totalrange of motion of the abutment, can also be adjusted.

The precise form of the device is affected by the pressure to which theswitch must respond, the permissible variation of such pressure, thecharacter of the control effected by the switch and similar details, buta switch intended to Open and close as pressure shifts across 3,000pounds per square inch is illustrated in the accompanying drawing astypical.

In the drawing- Fig. 1 is a plan View.

Fig. 2 is a section on the line 2-2 of Fig. 3.

Fig. 3 is a section on the line 3-3 of Fig. 1.

Fig. 4 is a view similar to Fig. 3 showing the switch reversed to reducethe sensitivity.

Fig. 5 is a fragmentary View similar to a portion of Fig. 4 showing adifferent :adjustment of the fulcrum The housing for the switchmechanism might be described as bottle shaped having a cylindrical bodyII which houses the switch mechanism and the neck l2 which houses thepressure responsive mechanism. The body II merges into v a mountingplate I3 with holes I4 for attaching screws. The lower end of the bodyII is closed by a removable plate I5 attached by screws.

The upper end of the neck I2 is threaded to receive a union fitting i5by means of which the pressure line I'l is placed in communication withthe bore lli above a pressure responsive diaphragm I9. This diaphragm ismade of some oil resisting rubber-like plastic and is clamped between aseat 2l and an annular seating disc 22 by means of a member 23 which isscrewed into the neck I2 from below and which serves as a clamp for thediaphragm and as a guide for 4the pressure stem 24.

This stem 24 has a domed head 25 which engages the central portion ofthe diaphragm I9 and which is limited in its downward motion by a ange28. A shoulder 21 bears against a spring seat 28. A 'coil compressionspring 29 reacts against the spring seat 28 and against a similar seatheld by'ring 3| threaded into the lower end of the neck l2. This islocked in its adjusted position by the locking member 32.

The stress on spring 29 is so adjusted that the plunger 24 will respondat the desired pressure, here assumed to be 3,000 pounds per squareinch. The stem 24 is guided in the spring seat 3| and extends throughthe locking member 32. Its lower end engages a lever 33 which is mountedwithin the body I I on an adjustable fulcrum.

This fulcrum comprises an eccentric journal 34 formed on the inner endof a screw 35 which is threaded into a boss 36 formed within the body Il(see Fig. 2). The lever 33 is held in assembled relation with thejournal 34 by a second boss 3l formed within the body Il. The screw 35is locked in its adjusted positions by a check nut 33.

The switch element is an ordinary micro-motion switch whose body appearsat 4l. It is tripped by depressing a push button or plunger 42 whichextends through a guide in its upper surface. The body 4I is mountedagainst the lug 39 and a companion lug 40 by a pair of screws 43. Theleads from the switch are indicated at 44.

As will be apparent from an inspection of Figures 3 and 4 the switch 4Imay be mounted in the body l l in either of two positions. In theposition of Figure 3 motion of the plunger 24 is multiplied so that thisis a high sensitivity setting. In the position of Figure 4 the motion ofthe plunger 24 is reduced giving a low sensitivity setting. In either ofthese positions the trip point 42 of the switch may be coordinated withthe motion of the plunger 2s by turning the screw 35 so as to raise orlower the axis of the journal 34 on which the lever 33 turns.

As indicated in Figure it is also possible to turn the screw 35 180degrees so as to position the journal 3s to the left of the axis ofscrew 35 instead of to the right thereof as is indicated in Figures 3and 4. This adjustment is one of minor eiect as compared to reversal ofthe switch body 4i.

In either arrangement it is possible toI raise and lower the axis of thejournal 34 so as to control the trip point of the switch, and theprecise pressure at which it trips.

The screws |15 (see Figures 1 and 2) are merely closure plugs and areneeded because tapped holes which receive the screws 43 must be drilledand tapped through from the outside of the case.

The invention provides a vary simple structure which may be manufacturedat moderate cost. The stress on the spring 29 may be readily adjusted byadjusting the spring seat 3|. By using interchangeable springs 29 ofdiiierent strengths a very wide range of pressures may be handled. Theadjustment of the journal 34 is effected by a very simple means andpermits a precise setting of the trip point of the switch. Theadjustability of the switch with reference to the lever permitsadjustment of sensitivity. While a very simple two position adjustmentis shown, it is obvious that any means permitting a shift of the pushbutton 42 in the direction of the length of the lever 33 might be usedto adjust sensitivity. The embodimeni-I illustrated is chosen for itssimplicity' and because it ciers a suiiicient range of adjustment forordinary commercial purposes.

What is claimed is:

l. In a pressure switch, the combination of a movable abutment; meansfor subjecting said abutment in one direction to a variable fluidpressure; yielding means for biasing said abutment in opposition to saidpressure; a snap acting switch; a mechanical connection between saidabutment and switch, and including a lever having a fulcrum; and meansfor shifting said fulcrum in a circular orbit.

2, In a pressure-operated switch, the combination of a movable abutment;means for subjecting said abutment to a variable fluid pressure, actingthereon in one direction; a spring serving to bias said abutment in theopposite direction; adjustable means for stressing said spring; a motiontransmitting member shiftable by said abutment; means for limiting themotion of said transmitting member; a snap-acting switch having anactuator shiftable past the trip point of the switch in both directions;a lever interposed between said transmitting member and said actuator;and a fulcrum for the lever shiftable to vary the relation of the trippoint of the switch to the position of said transmitting member.

3. In a pressure-operated switch, the combination of a movable abutment;means for subjecting said abutment to a variable fluid pressure, actingthereon in one direction; a spring serving to bias said abutment in theopposite direction; adjustable means for stressing said spring; a motiontransmitting member shiftable by said abutment; means for limiting themotion of said transmitting member; a snap-acting switch having anactuator shiftable past the trip point of the switch in both directions;a lever interposed between said transmitting member and said actuator;and a shiftable fulcrum for the lever, said fulcrum having at least twosettings in which respectively it establishes different motion ratiosbetween the transmitting member and the switch actuator, said fulcrumbeing shiftable in each setting in a direction to vary the relation ofthe trip point of the switch to the position of said transmittingmember.

MATTHEW W. HUBER.

